This application claims priority under 35 USC 119(a) to Patent Application No. 2004-267268 filed in Japan on 14 Sep. 2004, the content of which is hereby incorporated herein by reference in its entirety.
The present invention relates to copiers, facsimile machines, printers, and other electrophotographic image forming apparatuses; more particularly, the present invention pertains to a transfer apparatus employing endless belt(s) with which image forming apparatus(es) may be equipped.
Image forming apparatuses making use of endless belts have become widespread in recent years. Furthermore, endless belts are frequently utilized within image forming apparatuses at fuser apparatuses, transfer apparatuses, processing units, and the like.
For example, along with the increased speeds of color image forming apparatuses that have undergone rapid development in recent years, endless belts have been used as intermediate transfer bodies in the context of a technique in which image information that has been separated into respective hues is temporarily transferred to intermediate transfer body/bodies, such image information being printed in stacked fashion on intermediate transfer body/bodies, and these are all retransferred together from the intermediate transfer body/bodies on which such stacked printing was carried out and onto paper that is transported thereto from media supply tray(s). Furthermore, at transfer units which transfer developer to paper, endless belts are frequently used to improve transportability (i.e., tendency of paper to separate from photosensitive drum(s)) of paper that is transported thereto from media supply tray(s).
Endless belts utilized for such purpose(s) are subjected to application of electric field(s) at necessary region(s) thereof, prescribed electric field(s) causing developer to be transferred to intermediate transfer body/bodies and/or paper.
Such electric field(s) might be applied through utilization of either a technique involving application of electric field(s) under conditions of constant current or a technique involving application of electric field(s) under conditions of constant voltage, electric field application means in either case being constructed so as to employ roller-shaped electrically conductive component(s) (metal roller-like structure(s), roller-like electrically conductive rubber structure(s), etc.) to charge endless belt(s) with prescribed electric field(s) from back(s) of intermediate transfer body/bodies and/or paper.
The locus of contact between electrically conductive component and endless belt at such time is ordinarily such that the dimension in the width direction of the endless belt is greater than the dimension in the width direction of the electrically conductive component. The reason for this is so as to accommodate meander of the endless belt at either extreme side in the belt width direction (hereinafter “side(s)”) where the belt extends past the electrically conductive component and so as to compensate for transfer irregularities (e.g., wrinkling) arising due to the thickness of the belt. This being the case, despite application of an electric field to the electrically conductive component, as the sides of the endless belt extend beyond the sides of the electrically conductive component, not only will it be the case that the electric field at the endless belt does not act at either extreme side thereof but it will also be the case that the endless belt, which is under a prescribed amount of tension, will experience no load at either extreme side thereof.
However, because of meander and so forth of the endless belt, for example, developer from the photosensitive drum may, due to the electric potential to which the developer has been charged, also be made to adhere at either extreme side of the endless belt where the applied electric field does not act. Where this is the case, because the electric field does not act at either extreme side of the endless belt when a cleaning technique is employed in which a reverse electric field is applied to the endless belt to cause developer adhering thereto to be transferred back to the photosensitive drum, developer adhering at such locations cannot be cleaned therefrom.
Furthermore, it is common for either end in the width direction (hereinafter “end(s)”) of the electrically conductive component to produce bending at either side of the endless belt where there is no load, causing occurrence of cracking, tearing, and so forth toward the end of its service life. Moreover, there has been the problem that the endless belt engages in meander due to the fact that a portion thereof does not experience a load.
Various techniques have therefore been proposed to prevent such meandering of the endless belt.
For example, Japanese Patent Application Publication Kokai No. H04-42277 (1992; hereinafter “Patent Reference No. 1”) discloses art in which rib(s) projecting in circumferential direction(s) is/are provided at end(s) of metal roller(s), such rib(s) constraining meander of endless belt(s). Furthermore, Japanese Patent Application Publication Kokai No. H10-260624 (1998; hereinafter “Patent Reference No. 2”) discloses art in which thrust member(s) larger in diameter than outside diameter(s) of rubber roller(s) is/are provided at either end of corrective shaft(s), abutment of such thrust member(s) by end(s) of rubber roller(s) permitting prevention of meander. Furthermore, Japanese Patent Application Publication Kokai No. 2000-147950 (hereinafter “Patent Reference No. 3”) discloses art in which guide(s) provided at endless belt(s) strike flange(s) at end(s) of roller(s) and/or edge(s) of roller(s) on which such endless belt(s) is/are suspended, permitting prevention of meander.
As mentioned above, when the dimension in the width direction of the endless belt is greater than the dimension in the width direction of the electrically conductive component, the applied electric field will not act at either extreme side of the endless belt. However, because of meander and so forth of the endless belt, for example, developer from the photosensitive drum may, due to the electric potential to which the developer has been charged, also be made to adhere at either extreme side (uncharged region) of the endless belt where the applied electric field does not act. Where this is the case, because the electric field does not act at either extreme side of the endless belt when a cleaning technique is employed in which a reverse electric field is applied to the endless belt to cause developer adhering thereto to be transferred back to the photosensitive drum, it will be the case that developer adhering thereto cannot be cleaned therefrom. Developer adhering at either extreme side of the endless belt will consequently accumulate and this can act as an abrasive to abrade the surface layer of the photosensitive drum. Furthermore, markings in which photosensitive characteristics, manufacturing lot number, and/or the like for the photosensitive drum in question is/are inscribed might, for example, be embedded in portion(s) of the photosensitive drum surface layer located at either extreme side of the endless belt, such markings being capable of being read by optical sensor(s). This being the case, abrasion of the surface layer of the photosensitive drum might cause a problem to occur in which the optical signal is reflected in diffuse fashion at the surface layer portion of the photosensitive drum, making it impossible to properly read the markings.
On the other hand, with the aforementioned Patent Reference Nos. 1 through 3, while it is possible to prevent meander of the endless belt, there has been the problem that these are all constitutions capable of being applied where the dimension in the width direction of the endless belt is less than the dimension in the width direction of the electrically conductive component, but are not capable of being applied where the dimension in the width direction of the endless belt is greater than the dimension in the width direction of the electrically conductive component.
The present invention was conceived in order to solve such problems, it being an object thereof to provide a transfer apparatus and an image forming apparatus that will make it possible to simultaneously solve both the problem in which developer adhering at either extreme side of endless belt(s) accumulates to form abrasive that abrades surface layer(s) of photosensitive drum(s) as well as the problem in which meander of endless belt(s) occurs.